I found this page from Tonton Velo interesting, especially because I own several Le Chemineau bicycles. The world's first commercially available derailleur,( Le Chemineau), seems to have been largely forgotten, but it worked well, and lasts for a long time. I have been riding one for well over fifty years. Le Chemineau If this link doesn't work, it is the same as the one below that says Tonton Velo. If you Google Le Chemineau derailleur, most of the pictures you find are of my bikes. Not too many of the marque found their way to our shores.
West Hartford, Connecticut, USA